In an ozone generating apparatus in which ozone (O3) is generated using gas including oxygen as a material gas by using discharge, it is generally known such that nitrogen oxide (NOx) is by-produced when ozone is generated. Further, nitrogen oxides (NOx) which is by-produced is under the coexistence of ozone, most of nitrogen oxides (NOx) is present as the structure of dinitrogen pentoxide (N2O5). Dinitrogen pentoxide (N2O5) is a subliming material which becomes a solid at room temperatures lower than 30 degrees centigrade, therefore dinitrogen pentoxide (N2O5) easily changes its phase between a solid and gas. However, under ordinary operation conditions, it is very probable such that dinitrogen pentoxide (N2O5) is attached to almost whole area of a discharge space as a discharge product.
On the other hand, regarding general ozone generating apparatuses, a periodical check, which is performed once in three to five years, is recommended by suppliers. When a periodical check is performed, maintenance operation, in which all systems are halted, and further, ozone generating systems are opened to the atmospheric air, electrodes are taken out for cleaning, is performed. When an ozone generating apparatus to which solid N2O5 is attached is opened to the atmospheric air, it is concerned such that N2O5 reacts with moisture in the air, nitric acid (HNO3) is generated so as to corrode metallic materials. Especially, when electrode parts are corroded, at the time of restarting, ozone generation efficiency is reduced, and further, in some cases, a short circuit between electrodes may be caused. Further, a dew-point of a material gas is an important control factor. Moisture which remains the inside of an ozone generating apparatus after an ozone generating apparatus is opened to the atmospheric air or moisture which is accompanied by a material gas reacts with N2O5 which is generated in an ozone generating apparatus at the time of restarting and HNO3 is secondarily produced. Consequently, sufficient gas purge and lowering dew-point is necessary for an ozone generating apparatus.
A method for handling an ozone generating apparatus in which by using a water heating system so as to maintain heating an ozone generating apparatus tank, N2O5 which is attached to the inside of an ozone generating apparatus is vaporized to be removed, is disclosed (for example, refer to Patent Document 1), and it is proposed such that before an ozone generating apparatus is opened to the atmospheric air, N2O5 which is a factor for generating HNO3 is removed.
Further, with respect to an ozone generating apparatus in which gas is sealed in a tank, and an operation is stopped, an ozone generating apparatus, having means for circulating dry gas in order to prevent moisture entering from outside and prevent generating HNO3 in an ozone generating apparatus, is proposed (for example refer to Patent Document 2).
An ozone generating apparatus, in which in a case where an operation of an ozone generating apparatus has to be stopped without performing a proper stopping step such as emergency shut down, because an ozone generating apparatus needs to be opened to the atmospheric air immediately, in order to suppress corrosion of electrodes which is caused by HNO3 which is inevitably generated, at an end of an electrode tube corresponding to the side of entrance of a material gas, a gas flow amount controlling plug is provided so as to limit an amount of HNO3 which enters the inside of an electrode tube, and corrosion of electrodes which are arranged the inside of electrode tube is reduced, is proposed (for example, refer to Patent Document 3).
As above mentioned, the anxiety of corrosion of a metallic material which is caused by HNO3 in an ozone generating apparatus is discussed on the assumption that an ozone generating apparatus is opened to the atmospheric air, or an ozone generating apparatus is contacted with moisture in the atmospheric air, and measures are considered. In order to suppress corrosion of a metallic material, especially corrosion of an electrode which is caused by HNO3, it is important such that N2O5, which is a factor of corrosion, and moisture is not contacted with the inside of an ozone generating apparatus, in a case of a cylindrical multi-tube ozone generating apparatus, it is especially important such that N2O5 and moisture is not contacted with the inside of an electrode tube. Conventionally, accompanying of moisture is prevented by using gas having a low dew-point for an ozone generating apparatus, and after ozone is generated, before an ozone generating apparatus is opened to the atmospheric air, by adequately replacing gas in an ozone generating apparatus, remaining NOx is removed and an electrode part can be prevented from contacting with HNO3.